Yes, the 5LT does all the 5 or 6 do.
If you wanted to use a 6, you don't need to mount it in a bay, you can mount it anywhere in the case.
Is 6 not hard wired to use the LCD?
Also, if I dont have a front bay available, so will it most likely need to be mounted under or behind something.
As mentioned by Shoggy, the LCD panel can be removed if desired and you would have a 5 LT or 6 LT, Though you can interact with the 5 or 5 through the front panel, it is a bit of a pain because the menu system is basically binary, so lots of clicking/tapping.
The much preferred manner to interact with any aquaero is through the free
aquasuite program. The only requirement is that you connect the aquaero to the motherboard using a USB connection.
As to mounting, if you do not use a 5.25" bay slot, you may have to drill some holes elsewhere in the case to mount it.